McLaren reserve driver Kevin Magnussen says he was told the team were releasing him by email on his birthday.
Magnussen, who was 23 on 5 October, says he was informed by chairman Ron Dennis's personal assistant.
"It was a short paragraph explaining there would be nothing for me in the future. It arrived on my birthday, actually," he said.
The Dane raced for McLaren alongside Jenson Button in 2014 but was demoted after Fernando Alonso's arrival.
Dennis had initially chosen Magnussen to partner Alonso this season, but backed down when his fellow shareholder Mansour Ojjeh said he wanted to retain Button.
On Friday, McLaren put out a statement confirming their split with Magnussen.
In it, Dennis said Magnussen deserved a seat in F1 and said the team would do what they could "to help him successfully embark on the next chapter of his racing career".
Magnussen said he was not surprised to learn of his release, having told McLaren that he wanted to race next year, and realising there was no vacancy at McLaren with Alonso and Button staying.
The Dane, who finished second in his debut grand prix for McLaren in Australia in 2014, hopes to find a seat for next year and said he had had "good talks with a number of F1 teams and some of them are still going on".
His best chance is believed to be with the Lotus team, which is in the process of being taken over by French car giant Renault.
Among Magnussen's competition for that seat are former Toro Rosso driver Jean-Eric Vergne and Lotus's British reserve driver Jolyon Palmer.
There could be vacancies at the new US-based Haas team and at Manor.
However, Haas have signed the Franco-Swiss Romain Grosjean for one car and are expected to confirm shortly the recruitment of Mexican former Sauber driver Esteban Gutierrez.
Manor are likely to need drivers to bring a budget for a seat.
Belgian Stoffel Vandoorne, the new champion of the GP2 feeder series, is likely to take Magnussen's position as McLaren's reserve driver.
Magnussen beat Vandoorne, who is one of the most highly-rated young drivers not yet in F1, to the Formula Renault 3.5 title in 2013.